iscsi-target: Avoid holding ->tpg_state_lock during param update

iscsi-target: Avoid holding ->tpg_state_lock during param update

As originally reported by Jia-Ju, iscsit_tpg_enable_portal_group()
holds iscsi_portal_group->tpg_state_lock while updating AUTHMETHOD
via iscsi_update_param_value(), which performs a GFP_KERNEL
allocation.

However, since iscsit_tpg_enable_portal_group() is already protected
by iscsit_get_tpg() -> iscsi_portal_group->tpg_access_lock in it's
parent caller, ->tpg_state_lock only needs to be held when setting
TPG_STATE_ACTIVE.

Reported-by: Jia-Ju Bai <baijiaju1990@163.com>
Reviewed-by: Jia-Ju Bai <baijiaju1990@163.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>